The invention relates to a pultrusion processing method of nylon composites which uses the technology of long fiber-reinforced nylon anionic polymerization to produce nylon composite materials. The conventional pultrusion processing method basically employs thermosetting resins with low viscosity, such as unsaturated polyester, phenolic resins, epoxy resins and the like. For these thermosetting resin systems, many commercialized pultrusion machines and processes were developed to carry out commercialized production and to manufacture various finished products of thermoset plastic composites having structural strength.
Compared to short fiber-reinforced composites, thermoplastic composites are easy to store, with a long shelf life, the ability to be second molded and possessing mechanical strength. Therefore nations with advanced industrial technology are eager to research and develop the market for long fiber-reinforced thermoplastic composites. Traditionally, due to its excellent performance, short fiber-reinforced nylon composites have been broadly used. Similarly in various types of long fiber-reinforced thermoplastic composites, nylon composites whose development and product application research are also considered important are substantially potential generation of fiber-reinforced thermoplastic composites. In the preparation method for long fiber-reinforced thermoplastic composites, commercialized preparation methods are multi-step indirect methods. Wherein after polymerized thermo plastics are melted or dissolved, the final semi-finished products of thermoplastic composite materials are molded by means of autoclaving or impregnating reinforced fiber in second molding. For the autoclaved thermoplastic composites, because of the high viscosity of melt polymers, reinforced fiber cannot be wetted well enough. This lowers the bonding strength of interfaces between resin matrix and reinforced fiber which therefore dramatically reduces the composites mechanical strength and performance. The impregnation method of dissolved polymer solution which is necessary to dry away the solvent in impregnated composites is complex, wastes power and easily results in environment pollution. Therefore the preparation method for fiber-reinforced thermoplastic composites by impregnation in a polymer solution is not ideal.
See "RIM-Pultrusion of Thermoplastic Matrix Composites" by H. Ishida and G. Rotter in 43rd Annual Conference, Composite Institute, The Society of the Plastic Industry, 1988. Ishida et al. used caprolactam as reactant monomer, sodium hydride as a catalyst for anionic polymerization and phenyl isocyanate as initiator. After sodium hydride and phenyl isocyanate were reacted with a caprolactam catalyst composition and an initiator composition they were formed respectively and then individually added into the resin tanks of the high temperature reaction injection molding machine. After the catalyst composition was mixed with the initiator composition at high pressure, the mixture was injected into a resin impregnating tank to impregnate the glass fiber roving. Thereafter the fiber impregnated with nylon 6 reactant was drawn into a hot mold to polymerize nylon matrix and glass fiber-reinforced nylon 6 composites were obtained. However, the data of any mechanical strength of nylon 6 composites are not disclosed in this literature, therefore it is not understood whether the processing method described by Ishida et al. is possible in practice.
A method using in-situ pultrusion processing to produce fiber-reinforced thermoplastic composites is disclosed by J. S. HWANG and S. N. TONG et al. in 44th Annu. Conf. RP/C, SPI, 8-C(1988), wherein the main objective is to develop a new thermoplastic system and novel in-situ pultrusion processing equipment. In this paper, ABS resin is obtained by reacting liquid acrylonitrile-butadiene copolymer with styrene monomer, then this resin is injected into a heating mold to prepreg the reinforced fiber and cure it. During researching, it is found that the low viscosity of resins can make the fiber well prepreged, and it is important that the final product be remolded by heating. This method provides the resins which are both safe and convenient for treatment.
A pultrusion method to produce heat resistant carbon fiber-reinforced polyether imide composites having high performance is disclosed by Maywood L. Wilson and John D. Buckley et al. in 44th Annu. Conf. RP/C, SPI, 8-C(1988). The difference between this pultrusion processing and conventional pultrusion processing of thermoset resins is that monomer reactant and solvent are not produced during the polymerization in the pultrusion mold. Besides, in order to wet and cure reinforced fiber, the viscosity of conventional thermoset resins is in the range of about 500-1,000 cps and the temperature of the pultrusion mold is about in 300.degree.-400.degree. F. However, in the thermoplastic pultrusion processing method, the viscosity may be up to 1,000,000 cps or more and the temperature may be 800.degree. F.
The same RIM-Pultrusion molding method described above is continuously used to produce nylon composites by Xin Xing and Hatsuo Ishida in 1990 Annu. Conf., Composite Institute, The Society of the Plastic Industry, wherein nylon initiator in reactants of polymerization is changed with the pre-polymer obtainable by reacting polypropylene-oxide having the molecular weight of 4000 with hexamethylene diisocyanate. However, it doesn't show any data about common mechanical properties of finished products made of nylon composites. So the processing workability and the practical possibility of nylon composites can't be confirmed.
"A Study on the Properties of Continuous Fiber-Reinforced Nylon 6 Resin Composite Materials" is published by Chen-chi Ma and Meng-sung Yin in ROC Polymer Seminar Meeting 1988, wherein the polymerization of nylon 6 is conducted by the method of hydrolytic polymerization.